The present invention relates to an erasing method for an image recorded on a heat-sensitive recording medium used for prepaid cards and the like, which can be recorded on and later have the images erased by making use of a reversible transparency change dependent on temperature.
With the growth of the information society, recording media use many recording methods such as heat-sensitive recording, electrostatic recording, sparking recording, and electrophotography, have increased. When the media were recorded on once, the recorded images were maintained for predetermined periods. However, most of these recording media cannot be recorded on and erased repeatedly. Therefore, the media were treated as disposable goods, and were disposed of after use.
However, recently, many people believe that resources should not be wasted and that the environment should not be degraded. Therefore, it is hoped that recording media could be developed on which images could be recorded and erased repeatedly.
The recording media on which images can be recorded and erased repeatedly were disclosed in Japanese Patent Application, First Publication (Kokai), Sho 55-154198, and Japanese Patent Application, First Publication (Kokai), Sho 62-257883. The images recorded on the recording media can be recorded and erased by heating the medium, and the recorded images are stable at room temperature.
Recording/Erasing machines and thermal heads for the reversible heat-sensitive recording media were disclosed in Japanese Patent Application, First Publication (Kokai), Sho 57-8993 and Japanese Patent Application, First Publication (Kokai), Sho 57-94780, Japanese Patent Application, First Publication (Kokai), Sho 57-204580, and Japanese Patent Application, First Publication (Kokai), Hei 4-197658.
In these machines, to one dot of the thermal head is applied an amount of heat by an electric wave pulse. Images were erased by touching the thermal head to the image. In this case, the temperature gradient between the surface and deeper layers of the heat-sensitive recording layer of the reversible heat-sensitive recording medium becomes large, and the temperature of the heat-sensitive recording layer becomes in part outside of the transparent temperature range. Therefore, the heat-sensitive recording layer was treated so that the image was erased, although the heat-sensitive recording layer was maintained in an opaque state (milky white state) and the image was not erased adequately. In particular, a machine for prepaid cards, or tickets, such as a ticket machine, which must record at high speeds, has this problem.